The present invention relates to a stapler for driving staples into an object, such as a sheaf of papers, said stapler comprising a drive element arranged to expel a substantially U-shaped staple and drive its legs through said object.
When stapling a relatively thick sheaf of papers, a guide means is usually used for external guidance of the staple legs during the driving of the staple into the sheaf of papers. This guide means prevents the legs from bending outwards during the driving.
When stapling a thicker sheaf of papers or when stapling a sheaf of papers consisting of a comparatively small number of sheets of paper of a harder quality, e.g. sheets of paper of the type used for colour photocopies, the staple is slightly deformed in spite of the use of a guide means for external guidance of the staple legs.
When the drive element performs a driving stroke, i.e. is moved from an upper position to a lower position, its lower edge surface abuts against the web portion of the staple to press the staple legs through the sheaf of papers. When the driving resistance is too great, e.g. when the sheaf of papers is thick or when it consists of hard sheets of paper, the staple is deformed. This deformation consists in the upper portion of the staple legs sliding or creeping in under the drive element. During the continued driving stroke of the drive element, the staple then crumples up on the upper side of the sheaf of papers.
In an attempt to solve this deformation problem when stapling sheets of paper in a sheaf offering a considerable driving resistance to the staple legs, an underlying support for the web portion of the staple is used in a prior-art stapler. This support is connected with the drive element and follows it in its reciprocating movement. The support is pivotable about an axis, which is substantially parallel to the web portion of the staple, to be inserted under the web portion to form a support thereof, when the drive element abuts against the web portion of the staple during its driving stroke, and to be removed from its position under the web portion at the end of the driving stroke, before the web portion reaches the upper side of the sheaf of papers.
This solution functions fairly well and prevents a deformation of the staple of the kind described above, but it is complicated and takes up a relatively great deal of space.
In a known stapler, the deformation problem described above is solved in a considerably easier way by the drive element being provided with two protruding projections at the same mutual distance as the legs of the staple, which projections are arranged to engage the web portion of the staple just opposite a staple leg each, the projections being pointed in order to bite a distance into the web portion of the staple in the engagement therewith. By this design of the drive element, it is possible to drive the staples without deformation into sheaves of papers, which are considerably thicker than the sheaves of papers being stapable by means of prior-art staplers, which lack an underlying support for the web portion of the staple.